This invention relates to flow metering devices in general and to a clean grain flow metering apparatus for use on a combine harvester in particular.
When harvesting crop material with a combine harvester, the operator is not readily able to determine the amount of clean grain being gathered in relation to either the time being spent or the acreage being covered. This only can be determined subsequently, by physically weighing the grain obtained over a measured acreage during a given period of time. The only assistance given in this respect is by an acreage counter, which is provided on some combine harvesters to provide a cumulative measure of the acreage which has been harvested. Acreage counters are shown, for example, in GB. No. 1.358.178 and DE. No. 2.208.005.
However, with the various aids in the way of fertilizers and weed, pest and disease controllers presently available to farm management, it is very frequently required to subdivide the total acreage of the crop into smaller lots, which are treated differently from one another to test the effect of differing amounts and differing types of chemical aids. The results of differing treatments can be assessed properly only by the crop yield, but with existing crop measuring techniques it is extremely difficult for a farmer accurately to determine by experiment the treatment which is best suited to his land and farming methods.
Furthermore, with the advent of automation in combine harvesters, it also is necessary to have accurate on-the-go throughput signals which can be relayed to control various harvester functions, such as automated feedrate (ground speed) control system. On-the-go throughput signals also can be combined with grainloss signals to provide an instantaneous grainloss rate as a percentage of grain harvested.
Various attempts have already been made to provide a grain flow metering device. Some of the prior art devices provide volumetric measurements. However, weights and weight rates are preferred over volumetric measurements. Conversion of volume to weight is, of course, possible by using the specific weight figures for grain. However, exact specific weight figures vary greatly from crop location to crop location, such that, it is usually necessary to measure these values. In practice, it has been found that the conversion of volume to weight seldomly is done accurately and often is a cause for substantial errors. Examples of volumetric flow rate metering devices are found in EPC. No. 42,245 and DE. No. 3,045,728.
GB. No. 1.211.161 shows an impact counter wherein grain kernels are caused to impact against a sensor plate and the impacts are counted. However, this measurement principle cannot be used to produce a weight rate signal as the frequency of impacts is not proportional to the weight of the grain flow.
GB. No. 1.506.329 discloses a weight rate metering apparatus in addition to volumetric metering devices for use on a paddle type clean grain elevator of a combine harvester. The weight rate metering device comprises a spring loaded sensor plate which is mounted to swivel about its shaft and which projects into the path of the grain kernels at the discharge end of the clean grain elevator. Connected to the plate shaft is a potentiometer or the like which is coupled to an electronic signal processing circuit and to a display means. Depending on the variable quantity of grain which impinges on the plate and, on the kinetic energy of said grain, the plate is swung to a greater or lesser degree from its starting position opposite to the spring force acting thereon.
This results in the potentiometer generating a signal which is representative of the weight of grain actually being conveyed. It is remarked however that the sensor plate, which is mounted in the path of the grain, forms an obstruction to said grain flow which often causes plugging of the conveyor means. Moreover, the angular displacement of the plate is, by far, not proportional to variations in the flow rate as indeed, when the plate is in its initial position, a given increase in the flow rate will result in a much larger angular displacement of the sensor plate than when said sensor plate already assumes an inclined position.
The use of impaction as a method of measuring the weight rate of particulate material in general also is already employed in the farm machinery industry. In impact flow meters of this type, the material to be measured falls from a predetermined distance onto an impact sensing device which may comprise either a flat reflecting plate installed at an angle of about 30.degree. to the vertical in the flow path or a curved chute along which the flow of falling material is deflected. The forces exerted on the reflecting plate or curved chute are measured as an indication of the weight rate. These gravity impact flow meters have specific disadvantages which are described in greater detail below.